diff --git a/DESCRIPTION b/DESCRIPTION
index 3020709..4c93019 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -1,7 +1,7 @@
 Package: xfun
 Type: Package
 Title: Supporting Functions for Packages Maintained by 'Yihui Xie'
-Version: 0.50.4
+Version: 0.50.5
 Authors@R: c(
   person("Yihui", "Xie", role = c("aut", "cre", "cph"), email = "xie@yihui.name", comment = c(ORCID = "0000-0003-0645-5666", URL = "https://yihui.org")),
   person("Wush", "Wu", role = "ctb"),
diff --git a/NEWS.md b/NEWS.md
index 748eeed..09927a7 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -2,6 +2,8 @@
 
 - `tojson()` supports more types of data now, and will indent sub-elements for lists. See the help page [`?xfun::tojson`](https://git.yihui.org/xfun/manual.html#sec:man-tojson) for details.
 
+- Updated the default API key for `upload_imgur()` since the previous default key stopped working for some reason (thanks, @camille-s @jennybc, #97).
+
 - `upload_imgur()` shows the error message instead of the error code when it fails to upload the image, which is more informative.
 
 # CHANGES IN xfun VERSION 0.50
diff --git a/R/image.R b/R/image.R
index 05ddf1d..df7dc51 100644
--- a/R/image.R
+++ b/R/image.R
@@ -173,8 +173,8 @@ shrink_images = function(
 #' @param file Path to the image file to be uploaded.
 #' @param key Client ID for Imgur. It can be set via either the global option
 #'   `xfun.upload_imgur.key` or the environment variable
-#'   `R_XFUN_UPLOAD_IMGUR_KEY` (see [xfun::env_option()]). If neither is set,
-#'   this uses a client ID registered by Yihui Xie.
+#'   `R_XFUN_UPLOAD_IMGUR_KEY` (see [env_option()]). If neither is set, this
+#'   uses a client ID registered by Yihui Xie.
 #' @param use_curl Whether to use the R package \pkg{curl} to upload the image.
 #'   If `FALSE`, the system command `curl` will be used.
 #' @param include_xml Whether to include the XML response in the returned value.
@@ -183,9 +183,10 @@ shrink_images = function(
 #'   from Imgur (it will be parsed by \pkg{xml2} if available). See Imgur API in
 #'   the references.
 #' @author Yihui Xie, adapted from the \pkg{imguR} package by Aaron Statham
-#' @note Please register your own Imgur application to get your client ID; you
-#'   can certainly use mine, but this ID is in the public domain so everyone has
-#'   access to all images associated to it.
+#' @note Please register your own Imgur application to get your client ID. You
+#'   can certainly use mine, but this ID is in the public domain and it might
+#'   reach Imgur's rate limit if too many people are using it in the same time
+#'   period or someone is trying to upload too many images at once.
 #' @references A demo: <https://yihui.org/knitr/demo/upload/>
 #' @export
 #' @examples \dontrun{
@@ -201,10 +202,14 @@ shrink_images = function(
 #' options(xfun.upload_imgur.key = 'your imgur key')
 #' }
 upload_imgur = function(
-  file, key = env_option('xfun.upload_imgur.key', '9f3460e67f308f6'),
-  use_curl = loadable('curl'), include_xml = FALSE
+  file, key = env_option('xfun.upload_imgur.key'), use_curl = loadable('curl'),
+  include_xml = FALSE
 ) {
-  if (!is.character(key)) stop('The Imgur API Key must be a character string!')
+  if (is.null(key) || key == '' || key == '9f3460e67f308f6') {
+    i = floor(as.numeric(Sys.time()) %% 3) + 1
+    key = c("qyv(sq y 't)ws(", 'q (t"vxs%t "wr(', "xpyvq%vp'rwx)yq")[i]
+    key = decrypt(key, '1987052436fedcba')
+  }
   api = 'https://api.imgur.com/3/image.xml'
   hdr = paste('Authorization: Client-ID', key)
   if (use_curl) {
diff --git a/R/string.R b/R/string.R
index 062afce..c37337d 100644
--- a/R/string.R
+++ b/R/string.R
@@ -486,3 +486,11 @@ html_view = function(x, ...) {
 }
 
 one_string = function(x, ...) paste(x, ..., collapse = '\n')
+
+# en/decrypt a string via a character map (old and new must be 16 unique hex chars)
+.crypt = function(x, old, new) {
+  x2 = chartr(old, new, as.character(charToRaw(x)))
+  rawToChar(as.raw(strtoi(x2, 16L)))
+}
+encrypt = function(x, key) .crypt(x, '0123456789abcdef', key)
+decrypt = function(x, key) .crypt(x, key, '0123456789abcdef')
diff --git a/man/upload_imgur.Rd b/man/upload_imgur.Rd
index 427b672..0d9be03 100644
--- a/man/upload_imgur.Rd
+++ b/man/upload_imgur.Rd
@@ -6,7 +6,7 @@
 \usage{
 upload_imgur(
   file,
-  key = env_option("xfun.upload_imgur.key", "9f3460e67f308f6"),
+  key = env_option("xfun.upload_imgur.key"),
   use_curl = loadable("curl"),
   include_xml = FALSE
 )
@@ -16,8 +16,8 @@ upload_imgur(
 
 \item{key}{Client ID for Imgur. It can be set via either the global option
 \code{xfun.upload_imgur.key} or the environment variable
-\code{R_XFUN_UPLOAD_IMGUR_KEY} (see \code{\link[=env_option]{env_option()}}). If neither is set,
-this uses a client ID registered by Yihui Xie.}
+\code{R_XFUN_UPLOAD_IMGUR_KEY} (see \code{\link[=env_option]{env_option()}}). If neither is set, this
+uses a client ID registered by Yihui Xie.}
 
 \item{use_curl}{Whether to use the R package \pkg{curl} to upload the image.
 If \code{FALSE}, the system command \code{curl} will be used.}
@@ -40,9 +40,10 @@ document with \pkg{knitr}: you can set the \verb{knitr::opts_knit$set(upload.fun
 any more, and it is ready to be published online.
 }
 \note{
-Please register your own Imgur application to get your client ID; you
-can certainly use mine, but this ID is in the public domain so everyone has
-access to all images associated to it.
+Please register your own Imgur application to get your client ID. You
+can certainly use mine, but this ID is in the public domain and it might
+reach Imgur's rate limit if too many people are using it in the same time
+period or someone is trying to upload too many images at once.
 }
 \examples{
 \dontrun{